The present invention relates to the general field of hair dryers.
Typically, a hair dryer includes a tapered plastic shell between a rear end and a front end through which flows out the air set into motion and heated inside the hair dryer. The plastic shell thus defines at least one air inlet and one air outlet and is intended to accommodate at least one motor and one fan. Generally, the axis of the fan is borne by an internal structure attached in the central portion of the fuselage. It is known that operation of a hair dryer generates several types of noises among which are the noise related to the flow of the air flux and the noise related to the operation of the turbine used for generating the air flow.
A hair dryer thus comprises several sound sources respectively related to the turbulences of the flow of the hot air flux, to the noise of the turbine, in particular the rotation of the blades and to the noise related to the vibration of the motor coupled with the shell of the hair dryer.
As regards the noise source corresponding to the flow noise of the flux related to turbulences, it is observed that the observed turbulences are of any dimensions. This results in a noise having a rich wide band spectrum both in low and medium frequencies and in high frequencies.
As regards the noise related to the turbine, it consists of sound lines correlated with the speed of rotation of the turbine and with the number of its blades. Finally, the sound spectrum related to the vibration of the motor/shell connection is also a noise with spectral lines.
Thus, more specifically, the invention is interested in the use of an acoustic silencer within a hair dryer, this acoustic silencer giving the possibility of obtaining passive sound reduction, notably on the noise related to the air flow and in part on the noise related to the turbine.
Passive sound reduction devices are known in other fields. These devices use foams or else rock wool or glass baffles. These means may contribute to reducing a portion of the noise generated by the operation of the turbine, generally only the high frequency spectral portion, but it is found that these means are unsuitable for treating air flow noises.
In addition to this, it is not possible to use this kind of solution inside a hair dryer since there are risks of detaching particles from the acoustic material which cannot be contemplated from the point of view of health.
Inside hair dryers, the use of an acoustic grid at the air inlet usually placed at the rear end of a tapered plastic shell embodying the hair dryer, is thus known.
The fineness of the screen of this grid allows a certain number of sound frequencies to be filtered. Such a grid notably reduces the high pitch whistling sound of the turbine.
The major defect of such an acoustic grid is that it forms a significant obstacle to the air flow. Sound reduction is thus achieved at the expense of a detrimental pressure drop within the flow since the consequent pressure drop resulting from this is expressed by a loss of efficiency of the hair dryer. The hair dryer then produces less heated air for a given electric power.
Further, the acoustic grid only allows treatment of the noise on the air inlet. The noise transmitted by the air flow and the turbine to the outlet is therefore not considered.
Thus, existing solutions for reducing the noise, either cannot be installed inside a hair dryer for reasons of health or for reasons of ageing of the materials, or generate significant pressure drops destroying the efficiency of the hair dryer.